This invention relates generally to systems and methods for the measurement of properties of liquid samples.
Liquids, mixtures, solutions and reacting mixtures are often characterized using optical techniques such as photometry, spectrophotometry, fluorometry, or spectrofluorometry. In order to characterize samples of these liquids, the liquid is usually contained in a vessel referred to as a cell or cuvette, two or more of whose sides are of optical quality and permit the passage of those wavelengths needed to characterize the liquid contained therein. Recent applications require the characterization of very small liquid sample volumes. When dealing with very small sample volumes of, for example, from 1 to 2 microliters, it is difficult to create cells or cuvettes small enough to be filled and permit the industry standard 1 cm optical path to be used. The size of the cuvettes cannot be arbitrarily reduced since this results in increasing interference caused by the meniscus of the liquid, by the cuvette itself, by bubbles and other effects.
Several systems have been proposed to enable the measurement of very small liquid sample volumes. In one of the existing systems, a sample of the liquid to be examined is inserted, by means of a dispenser needle or other means, and retained between a light transmitter and a light receiver. In another one of the existing systems, the surface tension of a microliter or submicroliter sample of liquid is used to provide sufficient means to confine the sample between two substantially parallel surfaces on anvils spaced apart a known distance; two optical fibers penetrate the parallel surfaces and provide the light for the measurement.
It is desirable to insert a wavelength selective filter in the optical train in the vicinity of the measurement location in order to increase signal-to-noise. In the existing solutions described, a filter can not be inserted in the optical train in the vicinity of the measurement location.
There is, therefore, a need for a system for measuring properties of small volume liquid samples that allows the insertion of wavelength selective filters in the optical train in the vicinity of the measurement location.
There is a further need for a system that allows the insertion of selectable filters in the optical train in the vicinity of the measurement location.